The present invention relates to a process for making graft copolymers of polyolefins and alkyl acrylate. More particularly, the invention relates to melt grafting 2-hydroxyethyl methacrylate onto polyethylene and polypropylene resins.
Polyolefins such as polyethylene and polypropylene are non-polar polymers that, in general, are resistant to polar moieties. These polyolefins are customarily used commercially for barrier film applications. Such applications include product packaging to such commodities as disposable personal products like, sanitary napkins, diapers, adult incontinence products and the like.
Used polymers are typically disposed of by recycling, incineration or landfilling. Because of the increasing amount of material being sent to landfills it is becoming more important for the refuse to be biodegradable, compostable or both. In the area of disposable personal products, the outer polyethylene film layer has to be separated from the rest of the absorbent structure or the entire structure has to be comminuted.
Over the past decade or so interest has grown in modifying existing polymers to achieve commercially important copolymers having improved and, at times specific properties. This has been particularly evident in the drive to modify commodity polymers such as polyolefins with polar functional monomers such as acrylic acid and alkyl acrylates. For example, linear low-density polyethylene has been modified by melt grafting up to about 5 weight percent (wt. %) t-butylaminoethyl methacrylate (t-BAEMA) to produce a copolymer having improved properties for co-extrusion as tie layers. These tie layers are commercially important in the packaging and film industry to economically produce packages meeting specific requirements and sometimes governmental regulations.
Polyolefins have also been modified using acrylate esters such as methyl acrylate, 2-butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, octadecyl acrylate and corresponding esters of methacrylate.
Moreover, there is an increased emphasis on environmenlally safe coatings for plastics. These coatings are reducing the use of solvent based coatings and relying, to an ever increasing degree, on polar coatings such as water based materials. The utility of the graft copolymer of the present invention includes, but would not be limited to, materials having a greater affinity for a polar coating. Other uses may include wire coatings, injected molded articles and barrier films having increased mechanical compatibility between the graft copolymer of the present invention and hydrophilic compositions.
The production of the compositions has generally been accomplished by blending all the constituents into a monomer-coated resin mixture. The heterogeneous mixture of resin coated with monomer is then extruded, in the presence of a reaction initiator, to form a graft copolymer. This method has been successful to produce graft copolymers having a comparatively low weigh percent of grafted monomer. Moreover, the efficiency of grafted monomer to the polyolefin resin low, with an efficiency of less than 50 percent. Due to the grafting limitations and process inefficiency, there is a need for an efficient process that is capable of producing graft copolymers having a greater amount of monomer grafted to the polyolefin.